My guess the depletion of chylophyll. Oxidation reduces chylophyll.
I judge a green tea from the color of the spent leaf. Indian oolongs
are essentially black. Chinese oolongs are essentially green.

Jim

Lewis Perin wrote:
> For quite a while I've noticed that for lots of teas (e.g. young raw
> Pu'er, most oolong, first flush Darjeeling) the color of the leaves
> changes radically over the course of multiple steeps. Leaves that
> when dry are some shade of brown (most of the above) or multicolored
> (FFDJ, Oriental Beauty, some young shengs) gradually reach a uniform
> shade of green. This shade of green differs from tea to tea, but the
> direction of change over many steeps is the same.
>
> I've never read anything about this, let alone an explanation. Is
> there a clue, someone?
>
> /Lew
> ---
> Lew Perin /
> http://www.panix.com/~perin/babelcarp.html
> recent addition (thanks, corax): tianxia chacang